At Bundaberg, the Burnett River peaked at 7.9 metres overnight, its highest level since 1942 and water levels are expected to remain high for days.

"Bundaberg is now split in two," Deputy Mayor Tony Ricciardi told AAP, adding 100 homes and two dozen businesses had water above the floorboards.

About 400 people were evacuated overnight - most stayed with family and friends but about 100 headed to evacuation centres for the night.

"They're upset, it's Christmas and that. This is a one-in-100 year event, we won't see this again in our lifetime. Well, I hope," Mr Ricciardi said.

He said Bundaberg was the largest tomato growing region in Queensland, and many macadamia, avocado and sugar cane farmers would also be severely affected.

North, at Rockhampton, there are fears more than 4000 properties could be affected by what threatens to be one of the worst floods in the city's history.

Authorities say the Fitzroy River in the central Queensland city could reach 9.4 metres by Tuesday next week, and could even go beyond that.

Rockhampton Mayor Brad Carter says the council has no idea how many homes and businesses would be hit if levels reached that high or higher.

But modelling for a nine-metre peak, expected by Sunday, shows 150 homes would have water above floor level, 1000 homes with considerable water through yards, and 4000 parcels of land affected by water inundation.

"If it gets higher than that, the number goes up significantly at a greater rate," Mr Carter said on Thursday.

"It could be devastating," he said. "It is an extremely serious matter now."

Evacuations have not been ordered at this stage, but will be considered on Friday.

The river was at 8 metres at 11am (AEST) on Thursday and was expected to get to 8.5 metres during the day.

" .... supplies by road, rail and air will be cut come Saturday meaning we'll be completely isolated," he said, warning floodwaters could remain high until January 10.

"Evacuation centre preparations are in process and we will advise the community tomorrow or later today with details."

Ms Bligh told the ABC $5 million had already been donated to a national appeal set up on Wednesday to help flood victims across the state.